Devices Stop Most Power-Line Disturbances

Jun 1, 2008 12:00 PM
By David Morrison, Editor in Chief

A series of surge-protection devices from Innovolt protects electronic equipment from the many common power disturbances that transient voltage surge suppressors (TVSSs) based on metal oxide varistors (MOVs) cannot. The devices use the company's Current & Voltage Surge Suppressor (CVSS) technology to guard against voltage surges, current inrush surges, and overvoltage and undervoltage power disturbances. Moreover, they provide diagnostic functions, including a visual indication and record of power disturbances to the user, and also maintain an energy-consumption profile.

Innovolt offers its CVSS technology in a model for residential use (called the Plug In Protector) and three models for use with office equipment. Those office equipment models are named the Power Protector, the Power Manager and the Power Asset Manager, and offer different levels of functionality beyond the protection functions.

The Innovolt surge protectors overcome a basic limitation of TVSSs in that those devices only address the relatively rare power-line disturbances. For example, TVSSs protect against lightning strikes. However, lightning voltage surges are rather infrequent for most equipment on the order of one in 10 years, according to Innovolt. Similarly, the company notes that overvoltage events in the 138-V to 240-V range, which are clamped by MOVs, only occur about once a year. And while overvoltage events are rare, when they do occur, they can destroy MOVs.

Undervoltage events in the 60-V to 100-V range represent a slightly more common fault — these occur at a rate of one to two per year. The TVSSs do nothing to stop those events, which cause some loads to draw more current and overheat. Neither do they address the very common voltage sags, where line voltage falls into the 0-V to 100-V range for periods lasting up to 2 seconds. According to Innovolt, these events could be experienced 30 to 100 times in a one-year period. The voltage sags produce high inrush currents that result in thermal shock for many electronic components.

Innovolt's surge protectors overcome the TVSS limitations with a microcontroller-based approach to circuit protection (Fig. 1). The input to the surge protectors is a two-stage MOV that protects against overvoltage faults. It provides greater protection than the typical TVSS, which usually has a single-stage MOV. To protect the MOV itself as well as the load, the protectors use a PIC-based microcontroller with an on-chip analog-to-digital converter to detect the overvoltage condition and then activate an ultrafast relay that disconnects the load. The MOV can be disconnected in 4 msec once a dangerous voltage is sensed.

The same microcontroller also controls a current-inrush limiter that prevents current surges when an undervoltage condition is detected on the ac line. In addition, the microcontroller drives a display so that the end user of the equipment is alerted to any fault conditions and stores information on faults into nonvolatile memory (Fig. 2). The microcontroller also can track energy consumption, giving end users an automated tool for monitoring and minimizing energy costs.

According to Suresh Sharma, president and CEO of Innovolt, the challenge in developing the surge protectors was in packaging so much functionality into the device while maintaining affordability. Whereas a typical TVSS contains just a few capacitors and MOVs, Innovolt's residential product contains over a hundred parts. These components are densely packed onto three pc boards that can be assembled in parallel and then combined into a 7-in. × 2.5-in. unit, which is roughly the same size as a conventional surge protector. Pricing ranges from $75 for a 15-A version of the Plug In Protector to $357.50 for a 20-A version of the Power Asset Manager. For more information, see www.Innovolt.com.

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